1. Field of the Invention
The present invention relates generally to a gas turbine cooled blade and more specifically to a gas turbine cooled blade having a seal air supply passage for supplying therethrough a seal air from an outer peripheral side to an inner peripheral side of a stationary blade. The present invention also relates to a gas turbine cooled blade having a structure for enhancing a heat transfer rate in a cooling passage of a moving blade or a stationary blade.
2. Description of the Prior Art
Examples of the above-mentioned type gas turbine cooled stationary blade in the prior art will be described with reference to FIGS. 7 and 8.
FIG. 7 is a schematic cross sectional view of one example of a prior art gas turbine cooled blade, wherein FIG. 7(a) is a longitudinal cross sectional view and FIG. 7(b) is a cross sectional view taken on line III-III of FIG. 7(a). FIG. 8 is a schematic cross sectional view of another example of a prior art gas turbine cooled blade, wherein FIG. 8(a) is a longitudinal cross sectional view and FIG. 8(b) is a cross sectional view taken on line IV-IV of FIG. 8(a).
In an actual unit of the gas turbine, the number of stages is decided by the capacity of the turbines. For example, in a gas turbine constructed in four stages, its second, third and fourth stage stationary blades, respectively, have moving blades disposed in front and back thereof and each of the stationary blades is structured to be surrounded by adjacent moving blades and rotor discs supporting them. Hence, it is important that a main flow high temperature gas does not flow into a gap of each portion in an interior of the stationary blade, in which the gap is formed there during manufacture, assembly, etc.
As a countermeasure therefor, a construction is usually employed so that a bleed air from a compressor flows into the interior of the stationary blade from its outer peripheral side to be supplied into a cavity portion on an inner peripheral side of the stationary blade as a seal air. Thus, a pressure in the cavity portion is kept higher than that in a main flow high temperature gas path, thereby preventing inflow of the main flow high temperature gas.
The prior art example of FIG. 7 is of a seal air supply structure using a seal tube 4 for leading therethrough a seal air. The seal tube 4 is provided in a stationary blade at a position apart from an inner surface of a blade portion 5 to pass through a first row cooling passage A of a leading edge portion in the blade portion 5. Thus, a blade outer peripheral side communicates with a-cavity portion of a blade inner peripheral side so that a seal air 3 is supplied into the cavity portion through the seal tube 4.
Numeral 2 designates a cooling medium, which is supplied for cooling of the stationary blade to flow through the first row cooling passage A and further through a second row cooling passage B and a third row cooling passage C in the blade portion 5. The cooling medium is then discharged into the main flow high temperature gas from a blade trailing edge portion.
Also, another example in the prior art shown in FIG. 8 is constructed such that a sealing air 3 is supplied directly into a first row cooling passage A to be used both for a sealing air and a blade cooling air, wherein a seal tube such as used in the example of FIG. 7 is not used.
In the moving blade and stationary blade of a conventional gas turbine including those blades shown in FIGS. 7 and 8, there are provided cooling passages so that cooling medium is led to pass therethrough for cooling of the interior of the blade. By such cooling, gas turbine portions to be exposed to the main flow high temperature gas flowing outside thereof are cooled so that the strength of these gas turbine portions is maintained so as not to be deteriorated by the high temperature.
FIG. 9 is a longitudinal cross sectional view of the conventional gas turbine cooled blade. In FIG. 9, numeral 21 designates a-cooled blade (moving- blade), in which a cooling passage 22 is provided passing therethrough. Numeral 23 designates a cooling medium, which flows into the blade from a base portion of the cooled blade 21 to flow through cooling passages 22a, 22b and 22c sequentially and is discharged into a gas path where a high temperature gas 25 flows. A plurality of ribs 24 are arranged inclinedly on inner walls of the cooling passages 22a, 22b, 22c, as described later, so that the cooling medium 23 flows in each of the cooling passages as shown by arrow 29 with a heat transfer rate therein being enhanced.
FIG. 10 is an enlarged view of one of the cooling passages of the cooled blade 21 in the prior art as described above, wherein FIG. 10(a) is a plan view thereof and FIG. 10(b) is a perspective view thereof. As shown there, in the cooling passage 22 of the cooled blade 21, the plurality of ribs 24 are provided, each extending in an entire width W of the cooling passage 22 to be disposed at an incline with a constant angle 0 relative to a flow direction of the cooling medium 23 with a rib to rib pitch P and projecting a height e. The cooling medium 23 is led into the cooling passage 22 from outside of the cooled blade 21 to flow through the cooled blade 21 for sequential cooling therein and is discharged into the high temperature gas 25, as described in FIG. 9. At this time, the rib 24 causes turbulences in the flow of the cooling medium 23 so that the heat transfer-rate of the cooling medium 23 flowing through the cooling passage 22 is enhanced.
FIG. 11 is a schematic explanatory view of a flow pattern and a cooling function thereof of the cooling medium 23 flowing in the cooling passage 22 of FIG. 10, wherein FIG. 11(a) shows a flow direction of the cooling medium 23 seen on a plan view of the cooling passage 22, FIG. 11(b) shows a flow of the cooling medium 23 seen from one side of FIG. 11(a), FIG. 11 (c) shows the flow of the cooling medium 23 seen perspectively and FIG. 11(d) shows a heat transfer rate distribution in the cooling passage 22.
As shown there, in a space between each of the ribs 24, the cooling medium 23 becomes a swirl flow 23a as in FIG. 11(a) to flow downstream from upstream there so as to move in a constant direction along the rib 24 inclined as in FIG. 11(c). For this reason, as shown conceptually by the heat transfer rate distribution of FIG. 11(d), there is generated a high heat transfer rate area 30 on an upstream side thereof where the swirl flow 23a approaches a wall surface of the cooling passage 22 (boundary layer there is thin) . On the other hand, on a downstream side thereof where the swirl flow 23a leaves the wall surface of the cooling passage 22 (boundary layer there is thick), the heat transfer rate tends to lower as compared with the upstream side. As a result, there occurs a non-uniformity of the heat transfer rate according to the place, which results in suppressing enhancement of an average heat transfer rate as a whole.
In the first prior art example shown in FIG. 7, there is provided the seal tube 4 which is disposed at the position apart from the inner surface of the blade portion 5 for exclusively leading therethrough the seal air 3. Hence, in this system, while there is an advantage that the seal air 3, making no direct contact with the inner surface of the blade portion 5, can be supplied as the seal air before it is heated by heat exchange, there is also a disadvantage of inviting an increased number of parts and increased time in providing the seal tube 4.
Also, in the second prior art example shown in FIG. 8, while no such seal tube as the seal tube 4 is used and reduction of the parts and time can be realized, the seal air 3 is supplied passing through the blade leading edge portion where there is a large thermal load. Hence, there is needed a large heat exchange rate for cooling of the blade, which results in a problem that a temperature of the seal air becomes too high.
Further, in the prior art gas turbine cooled blade shown in FIGS. 9 to 11, the cooling medium flows to generate the swirl flow 23a which flows along the rib 24 in the cooling passage 22 as shown in FIG. 11(a). There are formed the high heat transfer rate area 30 in the place where the swirl flows 23a approaches the wall surface of the cooling passage 22, and the area of lower heat transfer rate in the place where the swirl flow 23a leaves the wall surface of the cooling passage 22 as shown in FIG. 11(d). Hence, the heat transfer rate becomes non-uniform to cause a lowering of the average heat transfer rate.